The present invention relates to a method of gasifying and combusting a carbonaceous fuel and, more particularly, to an integrated process wherein a sulfur and nitrogen-bearing carbonaceous fuel is gasified to produce a carbon monoxide-rich low Btu fuel gas with is subsequently combusted with additional carbonaceous fuel in a steam generating furnace.
Carbonaceous fuels, such as coal, peat, lignite and carbon-containing refuse, are abundant fossil fuel sources available for use in steam generating furnaces. However, due to the presence of nitrogen and sulfur compounds inherently in such carbonaceous fuel, the combustion of these fuels and steam generating furnaces create obnoxious gases such as nitrogen oxides and sulfur oxides which must be removed from the flue gas generated in the furnace prior to venting the flue gas to the atmosphere. One proposed method of utilizing carbonaceous fuel for steam generated generation in a more environmentally acceptable manner has been to gasify the carbonaceous fuel to produce a fuel gas which is treated for the removal of sulfur compounds therein and then fired in a steam generating furnace to produce steam and a hot flue gas having a lower sulfur oxide content.
One such method is presented in U.S. Pat. No. 3,818,869 wherein a steam generator is integrated with an on-sight coal gasification plant which produces a low Btu gaseous fuel for the steam generator from a high sulfur content coal. As disclosed therein, the high sulfur content coal is gasified in a reducing atmosphere to produce a low Btu fuel gas. This low Btu fuel gas contains unburned carbon and also hydrogen sulfide which is formed from sulfur contained in the coal. Therefore, this low Btu fuel gas is passed through a gas cleanup system wherein the char particles contained therein are removed and recycled to the gasifier and the hydrogen sulfide therein is chemically removed from the fuel gas to produce a clean fuel gas essentially free of particulate matter and sulfur compounds. This clean low Btu gas is then combusted in air in a steam generating furnace to produce a hot flue gas which has a low sulfur oxide content. This hot flue gas is used as in a conventional steam generator to produce steam for electrical generation or industrial purposes.
In order to produce a flue gas having a low sulfur oxide content in accordance with the above described process, it is necessary to provide a complex desulfurization system in order to remove the hydrogen sulfide from the low Btu fuel gas. The hydrogen sulfide is formed upon combustion of this sulfur-containing carbonaceous fuel in the reducing atmosphere of the gasifier. It is an object of the present invention to provide a method for the integrated gasification and combustion of a sulfur-bearing carbonaceous fuel wherein the step of processing the fuel gas produced in the gasifier to remove gaseous sulfur compound therefrom can be eliminated. Further, it is an object of the present invention to provide a method for the integrated gasification and combustion of carbonaceous material wherein a portion of the carbonaceous material is gasified to produce a low Btu content fuel gas which may be combusted in a steam generated furnace in conjunction with additional carbonaceous material to produce a fuel gas having not only a low sulfur oxide content but also a low nitrogen oxide content.